Extruder for manufacture of shaped bodies from plastics-filler mixtures having high filler content

ABSTRACT

An extruder forms shaped bodies from plastics-filler mixtures having a filler content of more than 50% by volume. The extruder comprises a product feed device, an outer mouthpiece and two barrels arranged coaxially between the product feed device and the outer mouthpiece. The first barrel (input cone) having an inside wall provided with grooves essentially parallel to the longitudinal extent of the barrel is connected with the product feed device. The second barrel (output zone) is connected with the outer mouthpiece. A screw arranged in the first barrel conveys material into the second barrel. Separate tempering arrangements for the first barrel, for the second barrel and for the mouthpiece control the desired operation temperatures in the extruder. Preferably, the extruder additionally includes a mandrel connected with the screw and arranged in the second barrel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 08/749,221, filedNov. 14, 1996, now U.S. Pat. No. 5,804,116, filed Sep. 8, 1998.

BACKGROUND OF THE INVENTION

The invention concerns a method for the manufacture of shaped bodies byextrusion moulding of plastic-filler mixtures containing more than 50%by volume of fillers and to an extruder for carrying out the method.

The property profile of plastics can be changed and as a rule improvedby the addition of fillers. Improvements of this type concern, forexample, the processability of the plastics or the properties of theproducts manufactured from such plastic-filler compositions such asE-modulus, impact strength, dimentional stability or heat resistance. Aslong as the content of fillers does not exceed a stipulated amount, noproblems occur in the shaping of the plastic-filler materials tointermediate or end products. Above a specific content of fillers, theflow qualities of such materials however degrade increasingly and theirprocessability becomes increasingly more difficult. This has especiallyproblematical effects on extrusion moulding. With high filler contents,the limiting transverse stresses necessary for generating a shearingflow rapidly become disproportionally high and very high forces arenecessary for the extruding. Extrusion of this type can only be handledwith a correspondingly expensive machine tool equipment, that is withspecial machines, and in many cases such materials generally cannot beextrusion moulded. Plastic materials with high filler contents have,moreover, a low melt dilatability. On emergence from the nozzle mouldingtool, damage like tearing or roughening or scaly surfaces thereforeoccurs, in particular with the extrusion moulding of flat bodies or evenof tubes.

SUMMARY OF THE INVENTION

The object underlying the invention, at least for a group of suchplastics containing high contents of fillers, is to make available amethod and an apparatus with whose help manufacture of defect freeshaped bodies, in particular of tubes or thin plates, but also of otherprofiles, is possible by extrusion moulding from such materials.

The object is solved by a method according to the presentabove-identified invention and by the making available of an extruder.In the respective claims which follow, advantageous embodiments of theinvention are indicated. The texts of the claims are accordinglyincorporated into the description of the invention.

DETAILED DESCRIPTION ON THE INVENTION

The invention concerns plastic-filler mixtures in which the fillercontents have a good thermal conductivity. Moreover it is restricted toplastic-filler mixtures with filler contents of more than 50% by volumeof filler related to the plastic mixture=100%. According to a preferredvariant, compositions of filler contents of more than 6% by volume, andespecially preferably those of 75% by volume and more, are processed.Plastic-filler mixtures with filler contents above 95% by volume are nolonger workable even by the described method.

Fillers for materials workable by the method according to the inventionare in particular non-graphitic and graphitic carbon like coke, carbonblack, synthetic and natural graphite, ground carbon reinforced withcarbon fibres (CFRC) or ceramic materials like silicon carbide (SiC),SiC infused with silicon (SiSiC), boron nitride (BN) and titanium oxidesof the type TiO, with n less than 0.5 or comminuted plastic reinforcedwith carbon fibres or metals, insofar as these are chemically compatiblewith the plastic of the material pairing provided. Preferably, granularand fibrous carbon-containing fillers and graphitic productsmanufactured in particular synthetically from these are used. Fillersmade from CFRC and CFRP are obtained by grinding of shaped parts formedof CFRC or CFRP. They consist as a rule of a mixture of carbon fibres,matrix substance and reinforced material remaining intact. The fillercomponent employed can also consist of mixtures of several fillers.

The dimensions of the particles used as fillers should not exceed theregion of a few millimeters. Granular/pulverous filler particles havepreferably a largest linear measured particle size of not more than 1mm. This holds in general also for fibrous filler particles.Nevertheless here it is suitable in many cases to work with fibres up tolengths of about 5 mm. Naturally, even larger filler particles can bemixed into the plastic, although this has the consequence that theseparticles become comminuted on grinding in method step 2. They are thenno longer completely encased in plastic. In the presence to a largeextent of broken surfaces not covered in plastic at the fillerparticles, especially with high filler contents, difficulties can occurin the later extrusion moulding.

All thermoplastic and thermosetting plastics as well as elastomers aresuitable for the working according to the method of the invention,insofar as they have a sufficient temperature resistance for the workingin softened state. Plastics employed are preferably thermoplasticallyprocessable fluorine-containing polymers such as co-polymers oftetrafluoroethylene with perfluoropropylene (FEP), co-polymers oftetrafluoroethylene with perfluoroalkylvinylethers (PFA), co-polymers ofethylene and tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF),polychlorotrifluoroethylene etc., polyolefines like polyethylene orpolypropylene, cycloolefine co-polymers like norbylidene-ethyleneco-polymers and other co-polymers of this type manufactured withmetallocene catalysts, polyamides, thermoplastically workablepolyurethanes, silicones, novolaks, polyaryl sulfides likepolyphenylenesulfide (PPS), polyaryletherketones which have a permanenttemperature resistance according to DIN 51 005 of at least 80° C.Plastics having a polyvinylidene and cycloolefinbasis are preferablyused. Also, mixtures of plastics combinable with one another can be usedif this is advantageous for example for improving the processability orthe optimising of the product properties.

For carrying out the first method step, the plastic and the fillercomponents corresponding to the specified charge are put into a heatablemixer and mixed there at least at the melting temperature of the plasticcomponents, preferably at temperatures at which the plastic has a lowviscosity sufficient for the mixing procedure, until the plastic ismelted and the filler particles are distributed uniformly over theentire mixture. Should it be necessary or important for the carrying outof one or several of the method steps for the properties of the endproduct, auxiliary materials like stabilizers, wetting agents, pigments,plasticisers or lubricating aids can be added to mixture before orduring the mixing process. Suitable as mixers are all discontinuously orcontinuously operating mixers which are able to work pseudoplasticmaterials which are very highly viscous as a consequence of large fillercontents. Coming into question here preferably are temperable, mostlyonly heatable, paddle or Z-arm kneaders with or without piston ram, or,for large amounts, e.g. double screw kneaders of the ZSK type orKo-kneaders. It is also possible to generate the energy required for theheating up of the material mechanically by use of mixing parts as aresult of shearing forces in the product to be mixed, although thismethod is generally not sufficient on account of the high heat lossresulting from the good thermal conductivity of the filler content.After the mixing, the mixture is removed from the mixer and allowed tocool.

In order to bring the plastic-filler mixture into a suitable form forthe extruding, in the third step of the method of the invention, it iscomminuted to particle sizes, or is graded after the comminution, toparticle sizes, which enable a working according to method step 4. Forthat, the material is initially broken up, where necessary, and thenground. In general, the material has however a consistency which permitsan immediate supply to a mill. Machines like pin beater mills or hammermills acting by means of impact action and which are especially suitedfor averagely hard to soft specified charges are preferably used forcomminution. In this method step, for reasons of economy, one shouldstrive to keep low the content of finely particulate fraction of below0.1 mm since too high a finely particulate content can hinder thedegassing in the subsequent working in the extruder. It is thereforeprovided, in known manner, that the grinding equipment is coupled with agrading arrangement and only the coarse particle component whichpreferably has a particle size of >1 mm is returned for furthercomminution in this arrangement. Where it is favourable, the limit forthe establishment of the coarse particle range can even be displaced tolarger values. According to a preferred variant of the invention,particles in the range of between 0.1 and 0.315mm are used for theextrusion moulding. According to another preferred variant, a materialto be mixed which has been coarse crushed in suitable manner is chargedto a mill, the material is ground down in this by a "bulk grinding",after which, should it be necessary, the fine grain part of it lyingbelow 0.1 mm mesh is reduced by grading to a content of less than 25% byweight and this bulk ground material is supplied to the fourth methodstep.

The plastic-filler mixture obtained by the third method step, comminutedand possibly graded, is remelted in the fourth method step and extrusionmoulded to form profiles. For carrying out this method step, an extruderwith conveying input zone, also termed as extruder, with grooved inputzone or grooved barrel extruder or grooved extruder, is used. Thecharacteristic of this type of extruder is the provision of longitudinalgrooves in the cylinder wall, the grooves being provided essentiallyparallel to the longitudinal extent of the screw in the entry zone ofthe extruder, which grooves end conically as a rule at the end of theentry zone, seen, that is, in the conveying direction. The cross sectionof the grooves is conventionally rectangular, but it can, depending uponspecial technical circumstances, also have other forms. The processtechnology speciality of this type of extruder is that the bulk chargeintroduced into the input and conveyor chamber of the extruder keys formfittingly into the grooves, whereby the coefficient of friction of thematerial increases strongly at the cylinder wall and accordingly adisplacement of the material in the peripheral direction is madeimpossible. The material is therefore conveyed practically exclusivelyin the axial direction as a result of the forces acting over the thrustsurfaces of the screw. In the procedure according to the state of theart, the material is cooled or only slightly tempered in the groovedinput zone, because it is not to form any melt film on the cylinderwall. Nevertheless, should this occur, the advancing of material wouldbe brought to a standstill because the coefficient of frictionmaterial/barrel wall will become too low with respect to that of thepairing screw/material and the material would only continue to go roundand round in the cylinder of the input zone as a consequence of this. Incontrast, with the method according to the invention, the groovedbarrel, and where it is required, also the screw is adjusted by suitableheating arrangements to a temperature which, in the case of amorphousplastic, is above the glass transition temperature and, in the case ofpartly crystalline plastics, above the crystalline melting range of theplastic used. As a result, the granular plastic-filler materialintroduced into the input zone of the extruder is heated by heattransfer from the surfaces of the cylinder of the input zone, andpossibly the screw, which could be contacted by the material and by thefriction at the aforementioned surfaces being generated with theadvancing procedure in the input zone and the material is compacted atthe it i s not necessary to heat the end of this zone. In general, it isnot necessary to heat the screw and, with especially strong frictionbetween the material and the surface of the screw, it can even bepossible that heat must be removed via the tempering arrangement of thescrew. With the conveying and compacting procedure taking place in theinput zone, it is necessary for care to be taken, for example by meansof a suitable gradation of grain sizes of the material supplied to theinput zone, that the material is de-aerated sufficiently, that is thatthe gas located in the charged material can be vented in the directionof a venting opening, for example the feed pipe. As a consequence of thegood thermal conductivity of the plastic-filler material according tothe invention, a good heating up of the material to be processed islargely achieved, although a pure plug flow is present and practicallyno dissipation energy is introduced to the material. On account of thisgood compaction and heating through already at the end of the inputzone, the plasticizing or compression zone in which takes place afurther homogenisation of the material can follow the input zonecomparatively shortly. According to the invention it is also notnecessary to provide in this zone, besides a normal screw formation,special shearing or kneading elements. At the transition from the inputzone to the plasticising/homogenising zone, however a thermal barriermust be present. By thermal barrier is meant a thermal insulation of theheater(s) and, so far as is technically possible, all the heat transferelements between the processing zones of concern. It is thus possible tomatch the temperature of the material located in the extruderindividually to the requirements in the separate processing zones. Inthis second processing zone, the temperature control must be so adjustedthat the material is continuously thermally homogenised.

The output zone carrying at its end the nozzle shaping tool ormouthpiece follows the plasticising/homogenising zone, which isconstructed according to the state of the art. It must be equipped witha controllable heater in order to be able to set optimum temperatureconditions from the extrusion moulding procedure. Also, between theplasticizing/homogenising zone and the output zone there is provided athermal barrier. In the output zone, the material plasticized andthermally homogenised in the previous steps is to be removed by means ofthe pressure built up onto the mouthpiece at the mouth piece-side end ofthe input zone and shaped by this to a shaped extrudate. Forfull-section profiles, mouthpieces of usual constructional form areused. For the extrusion moulding of tubes, mouth pieces with a weblessheatable mandrel are employed. The mandrel is here formed as anextension of the screw of the extruder and rotates with this. It isequipped with one of the controllable heaters known from the state ofthe art, by means of which a mandrel temperature can be adjusted whichguarantees as low as possible a co-efficient of friction between thematerial to be extruded and the mandrel surface. Should it be necessary,the wall inside of the tube mouthpiece, similarly to the inner wall ofthe cylinder of the input zone, is provided with longitudinal groovesrunning in the direction of the mouthpiece opening in order to preventrotation of the material in the mouthpiece. Mandrels held by means ofwebs in the mouthpiece cannot be used for the aforementionedplastic-filler material since the material flowing through the mouthpiece is divided at the webs and as a consequence of its low capacityfor melt working would not become connected with one another again, atleast not again perfectly, beyond the webs.

With plastic-filler materials with especially high contents of fillersor those with relatively large filler particles, there remain after thecomminutions carried out in the third method step, "free" break surfacesnot covered with plastics. These break surfaces can be causes ofdeficient flow behaviour of the material in the extruder and for a badcapacity of the plastic-filler material to bind with one another or becoherent. Difficulties of this type can, where this is made possible bythe properties of the later manufactured product, be met by supplying tothe comminuted or comminuted and graded material the same type ofplastic, preferably in finely divided form in an amount whichcorresponds approximately to the covering requirement of the surfaces ofthe filler particles existing free as a result of the comminution.Moreover, the necessary amounts of plastic to be added amount to up to80% by weight related to the plastic-filler material provided for theextrusion. Which amounts must be used exactly must be determined fromcase to case by the man skilled in the art by means of simply carriedout extrusion experiments.

The low melt workability or melt extendability of the materialsprocessable in this process also does not allow the extrusion mouldingof relatively wide webs or plates with a small ratio of height to width,that is of flat webs or plates to take place e.g. through a wide slitnozzle, since faults arise on extrusion, especially cracks extendingfrom the middle of the plates. Manufacture of webs or plates of thistype is possible nevertheless according to a variant of the invention ifthe material is extruded through a mouthpiece for the extrusion mouldingof a hollow profile having curved outer and inner contours and the wallof the hollow extrudate emerging from the mouthpiece, as long as this isstill deformable, is split at at least one side along its entire lengthand the cut hollow extrudate is bent flat to form a web and this is cutthrough, possibly afterwards, to plates of desired length. Clearly,plates can also be manufactured according to this method by splittingthe walls of corresponding hollow profiles at a later time along theirlength and shaping the bodies thus obtained into plates. Certainly thenthe hollow profile or the cut hollow profile must first of all be heatedagain to the shaping temperature. A similar method for the manufactureof webs or plates together with the extruding of hollow profiles hasbeen previously described in JP-OS-06-060886. Different to the methodaccording to the invention described here, necessary for the manufactureof extrudable materials in the named specification is always theaddition of solvents, disperants or special binders which must first ofall be removed by drying/vaporisation after the shaping.

Plates or webs which have been manufactured according to the presentinvention can be provided on either one or both surfaces with a profile.Should it be convenient, this happens directly in association with thepassing out from the extruder as long as the web still has a sufficientplasticity, thus is in the hot state. According to one possibility,moreover, the profile is impressed by pressing a heated embossingroller(s) acting on the extruder web or on the plates with one on oneside or with two rollers from opposite sides, according to whether theembossing is only to be employed on one side or on both sides of thesurface. According to another method, heated embossing stamps are usedwhich can act on one or both sides or which impress the profile in amatrix whose base carries possibly a counterprofile. Still furtherprocesses for the incorporation of a profile are known and used by theman skilled in the art. For example, the profiles can be worked onprogramme controllable operating machines even after the completesolidification of the webs or plates by machine working. According to afurther variant of the invention, one or both surfaces of the web or ofthe plates can be provided with a coating which lends to the surfacesspecial, for example electrical, chemical, mechanical, optical or colourproperties. Here, especially preferred is the application of acatalytically, in particular an electrochemically acting catalytic layerwhich contains or consists of for example metals or metal compounds ofelements of the VIIIth sub-group of the periodic system of the elementsor electrically semi-conducting substances. According to a furtheradvantageous variant of the invention, the coating is provided at thesame time as the embossing procedure, for example by having anapplication devices like rollers, brushes or spray arrangements,connected after or prior to the embossing step, or it takes place bymeans of the embossing tool itself.

In the method described as aforesaid, an extruder is used which is knownin principle in plastic working is technology. The invention consists inthe combination of the features of the method procedure with thetechnical construction of the extruder specially matched thereto.

According to an especially preferred variant of the invention, themethod is carried out with use of a modified grooved barrel extruderwhich consists merely of two zones between the product feed devices andthe outer mouthpiece end, namely the input zone and the output zonecarrying the nozzle shaping tool. Arrangements like filling hoppers,belt weighers etc. known to the man skilled in the art can be used asproduct feed devices. As with known machines with conveying input zones,here too the cylinder is equipped in the input zone on the productguiding side with longitudinal grooves which effect in the previouslydescribed manner, in cooperation with the screw, an automatic conveyingof the material conveyed via the feeding arrangement into the inputzone. The screw ends at the end of the input zone. Only the shaft of thescrew extends to some extent into the output zone. In the case of theextrusion of tubes, it is guided to a mandrel at its furthest up to theend of the mouthpiece, with reduction in its external diameter. Theshaft of the screw and in particular its part located in the output zoneare provided with a tempering, preferably a heating arrangement. Theoutput zone follows the input zone without connecting in between aspecial plasticizing, homogenising or compression zone. It is howeverimportant for carrying out the method that between the input zone andthe output zone there is provided a thermal barrier. By means of this,the temperature pattern in the two zones can be controlled independentlyof one another. If for example the temperature of the material at theprocess-side end of grooved barrel zone would become too high, e.g. as aresult of the friction taking place there, sufficient heat must beremoved in the zone that the material is not damaged. However, thetemperature of the material must be kept sufficiently high in the outputzone which follows for this to be sufficiently fluid so that a regularpressing-out is guaranteed. It must thus be heated there. In carryingout the method, the plastic-filler material is taken up in the inputzone and during its transport is compressed increasingly in thedirection of the output zone subject to continuing de-aeration. At theprocess-side end of the input zone, the material is then practicallycompletely de-aerated and the pressure controlling it reaches itsmaximum. The material is conveyed into the output zone under thispressure and is extruded therethrough the mouthpiece subject to"pressure loss". On account of the great compaction of the materialalready at the end of the input zone, care must be taken that theleading away of the gases located in the granular delivery feed, ingeneral air, is made certain in the input zone. Apart from measuresappertaining to apparatus known to the man skilled in the art, thishappens as a result of the suitable choice of particle composition ofthe supplied feed, described in the foregoing. A special feature here isto maintain use of a not too high fines content. Differing from theextrusion method according to the state of the art, according to apreferred method variant of the invention, the mixture stipulated forextrusion is already heated in the input zone to temperatures above themelting range of the plastic used as matrix material. By the termmelting range is understood, with plastic with crystalline components,the range of the crystallite melt temperatures and, with amorphousthermoplasts, the glass temperature. The material may not however beheated so high that, in the input region, there is formed on thecylinder wall a low viscosity film of plastic melt on which theremaining plastic-filler material can slide. In such a case, anyconveying of material in the conveyor might come to a standstill. Thetemperature rise and heating through of the material in the extrudertakes place both in the input and also in the output zone by heattransfer from the surfaces of the heated cylinder and possibly the screwor from those surfaces of the casing located in the output zone and themandrel, by the friction of the material on the surfaces of thepreviously indicated components of the equipment and by the good thermalor temperature conductivity of the material. A heating increase bydissipation does not takes place in practice. Where overheating of thematerial could occur there as for example at the end of the input zonebefore the thermal barrier to the output zone, a possibility for theremoval of heat from the material must be provided.

The extrudates manufactured according to one of the method variantsdescribed in the foregoing have, besides the properties resulting fromtheir composition of stipulated plastic and fillers, good thermalconductivity and electrical conductivity properties. They are thereforepreferably used as components for heat exchangers, for electrodes whichare thermally lightly loaded, for example in electrochemical detectionor separation methods like electrolysis, in batteries or in fuel cellsor for electrical purposes like heating elements or components forscreening of electrical fields or for the dissipation of electricalcharges. Plates manufactured according to the invention are usedpreferably for heat exchangers and plates equipped with catalyticallyactive coatings are preferably used for fuel cells.

In the following, the invention is explained further by means ofexplanatory examples:

EXAMPLE 1

For the manufacture of the plastic-filler mixture, 768 g of groundelectrographite, particle fraction 0.04 to 0.20 mm,

432 g of ground electrographite, particle fraction less than 0.01 mm,and

300 g of PVDF granulate, Solef 1010 type from Solvay-Kunststoffe GmbH,corresponding to 76.6% by volume (80% by weight) filler content and23.4% by volume (20% by weight) plastic component

were kneaded in a piston ram mixer, LDUK1 type, manufacture Werner &Pfleiderer, for 10 minutes at a temperature of 230° C. while subject topiston ram loading.

After discharge from the mixer and cooling, the material was ground in afine impact pulveriser, UPZ24 type, manufacturer Hosokawa Alpine AG, andfractions less than 0.1 mm and 0.1-0.315 mm were screened from theground product. Then a homogenised mixture of 15% by weight of theparticle fraction of less than 0.1 mm and 85% by weight of the particlefraction of 0.1 to 0.315 mm was extruded by means of an extruderaccording to the invention consisting, with reference to the partscontacted by the product, merely of supply arrangement, input zone andoutput zone (inclusive of mouthpiece), extrusion taking place through atubular mouthpiece with a casing internal diameter of 27 and a mandrelexternal diameter of 25 mm. The mandrel was not held by webs, but wasconnected, as one, with the conveyor screw of the input zone. Theextruder was equipped with a single thread screw having a diameter of 30mm, a pitch of 15 mm (=0.5 d) and a pitch depth of 2.5 mm. The casinginside of the cylinder of the input zone had, seen from the middle ofthe supply hopper, six 90 mm long (=3 d) conically extending rectangulargrooves with an inclination of 2° 11 minutes in the direction of theoutput zone. The input zone was tempered as 210° C., the output zone at240° C. The tubular extrudate was continuously cut at one side duringthe emergence from the mouthpiece by a knife secured at the end of themouth piece and was bent flat to a web. Then the web was cut into plateshaving a length of 100 mm and the plates thus obtained were provided onits sides with longitudinal and transverse grooves in a roller embossingarrangement with a temperature of 230° C. The plates had the propertiesdenoted in Table 1, under Example 1. After the finishing, they were usedas bipolar electrodes in a fuel cell.

EXAMPLE 2

For the manufacture of a plastic-filler mixture, the followingcomponents were kneaded in a driven kneader with sigma-paddles initiallyfor 15 minutes at 220° C. without exertion of pressure by a ram and thenfor a further 5 minutes at the same temperature with pressure applied bya ram:

835 g of electrographite, particle fraction of 0.04 to 0.2 mm

470 g of graphite powder KS 75, manufacturer, Lonza AG and

195 g of COC-plastic (cycloolefinpolymer), COC 5013 type, manufacturerHoechst AG, corresponding to a plastic content in the overall mixture of24.3% by volume (13% by weight).

After emergence from the mixer and being allowed to cool down, thematerial present in the form of pellets was ground on a pin beater atroom temperature and the ground material was graded. Then a homogenisedmixture of 24.75 parts by weight of the particle fraction of less than0.1 mm, 74.25 parts by weight of the particle fraction 0.1 to 0.315 and1 part by weight of plastic-based pressing auxiliary, PED 153,manufacturer Hoechst AG was extruded in an extruder, in principle asdescribed in Example 1, through a tubular mouthpiece having the samemeasurements as in Example 1. Differing from Example 1, however, adouble screw with a screw pitch of 30 mm was used. The temperature ofmaterial in the output zone amounted to 260° C. As previously describedin Example 1, the curved surface of the tubular extrudate was cutcontinuously down one side in the longitudinal direction on emergingfrom the mouthpiece and the former tube was bent flat to a flatextrudate on a support tempered to 240° C. The plates obtained then fromthe extrudate by cutting and having a length of 80 mm were provided byan embossing tool with a grooved profile in a die press with heatabledie at a temperature of 250° C. under a pressure of 150 bar. Thephysical characteristics of the plates thus obtained are to be seen fromTable 1, under Example 2. Plates of this type were used as electrodesfor electrolysis purposes.

EXAMPLE 3

For the production of the extrudable mixture, in this case 82% by weightof electrographite, particle size less than 0.5 mm were mixed with 18%by weight (=28% by volume) of novolak powder of 222 SP type,manufacturer Bakelite AG, flow limit at 125° C., 55 to 70 mm (DIN16916-02-A), which contained 8% by weight of hexamethylenetetramine ashardener, in a Z-Arm-Kneader at room temperature. After emergence fromthe mixer, the mixture was extruded in an extruder as has been describedin Example 1 and through a mouthpiece for the manufacture of tubes at amouthpiece temperature of 80° C., the mouthpiece having measurements 25mm external diameter and 22 mm internal diameter. The tubular extrudateemerging from the mouthpiece was then separated lengthwise into twoequal halves by means of a cutter exceeding the external diameter of thetube and attached directly to the mouthpiece but not connected with thecentral mandrel of the mouthpiece, and these halves were bent flat toform strips and then cut to plates 100 mm in length. The space in frontof the mouthpiece in which the aforementioned manufacture of the platestook place was tempered to about 75° C. by means of a heated table. Theplates thus produced were reshaped in a die press at a temperature of120° C. and a pressing force of 100 bar to ribbed electrodes and thenfinally hardened at 180° C. The physical characteristics of the platesthus produced are indicated in Table 1, under Example 3.

EXAMPLE 4

For the manufacture of the plastic-filler mixture, 1408 g ofcommercially available titanium powder, titanium content 99.9%, particlesize up to 0.150 mm (up to 100 mesh) were kneaded in a nitrogenatmosphere with 80 g=5.4% by weight or 22% by volume of a polypropylenegranulate, Eltex PTL 220 type, manufacturer Solvay Kunststoffe GmbH in aZ-Arm-Kneader equipped with piston ram while subject to piston ramloading. After emergence from the mixer and after being allowed to cool,the mixture was ground in a slowly operating impeller mill, likewiseunder nitrogen as protective gas against danger of ignition andexplosion, and the fraction of less than 0.4 mm was separated off forthe subsequent extrusion. This extruding was carried out by means of anextrusion arrangement according to Example 2 having a tubular mouthpiecefor tubes having the measurements, external diameter 25 mm, internaldiameter 22 mm, which was heated to a temperature of 220° C. and whosemandrel was likewise kept at a temperature of 220° C. The tubesmanufactured in this way were employed, after a mechanical finishing, asmeasuring electrodes for potential measurements. The physicalcharacteristics of such tubes are indicated in Table 1, under Example 4.

EXAMPLE 5

For the manufacture of the plastic-filler mixture, 1430 g of copperfibres, diameter 10 μm, length 2 mm, were mixed with 70 g=4.5% by weightor 20% by volume of PVDF powder, Solef 1010.6001.1 type, manufacturerSolvay-Kunststoffe GmbH, at room temperature with a stirrer blade, likethat used also in domestic mixers. The mixture thus obtained wasthereupon extruded by means of an extrusion arrangement according toExample 1 with a mouthpiece temperature of 240° C. to form a solidextrudate of thickness 1.5 mm, width 10 mm. After the cutting up of theextrudate to the respective desired lengths, the strips thus obtainedwere used as potential compensators. The physical characteristics ofthis product are to be seen from Table 1, under Example 5.

In the following, the invention, in particular the arrangement forextruding, is explained further by way of example by means of figures inschematic representation.

FIG. 1 shows a longitudinal section along the central axis of anextruder according to the invention having conveying input zone.

FIG. 2 shows a transverse cross-section through the input of a tubularmouthpiece with a rotating mandrel along the line II--II of FIG. 1, themouthpiece being provided with grooves.

In FIG. 1, there is shown an extruder (1) with conveying input zone (2)(grooved barrel extruder), which consists essentially of a machine frame(3) reproduced only schematically, a likewise only schematicallyreproduced drive unit (4) for the shaft (7) equipped here with a toothedwheel and the shaft (7) being coupled via adjusting springs (17) to thescrew (5), an output zone (11) and tempering arrangements (8),

1. for the groove barrel (9) in the input zone (2), (8'),

2. for the screw (5) in the input zone (2), (8"),

3. for the mouthpiece (10), (8'"),

4. for a mandrel (6), (8""), located in the mouth piece (10).

The measuring and controlling arrangement likewise necessary for theoperation of the extruder, as well as further peripheral arrangementslike for example a removal arrangement for the extrudate are state ofthe art and are therefore not shown. The characteristic of the extruder(1) is that its parts contacted by product, with the exception of thesupply arrangement (12) for the product to be extruded, which is shownhere as a filling hopper (12), consist merely of the input zone (2) andthe output zone (11). A homogenising or compressing zone is absent. Afurther important feature is the presence of a thermal barrier (13)between input zone (2) and output zone (11). The wall inside of thecylinder (9) of the input zone (2) is equipped with six conicallyextending grooves (14) of rectangular cross section at the mouthpieceend (2') of the input zone (2), of which only two are to be seen in thepresent representation. Furthermore, the cylinder (9) contains channels(15) for the conducting therethrough of heat conducting medium fortempering, essentially for heating, the grooved bushing (9) (temperingarrangement 8'). This tempering arrangement (8') can also consist ofmore than one zone in order to be able to temper material to be extrudedin a more targeted manner. Optionally, the material is evenly cooled inthe neighbourhood of the mouthpiece side end (2') of the input zone (2)for avoidance of harmful overheating. The single screw (5) located inthe input zone (2) is internally hollow. The screw (5) can be equippedwith a tempering arrangement (8") suitable for cooling or heating andoperating with a heat conducting medium. The tempering arrangement (8'")of the output zone (11) consists of a heating jacket. The mandrel (6)provided for when extruding hollow extrudates and connected fast withthe screw (5) and positioned centrally in the mouth piece (10) contains,as tempering arrangement (8""), an electrically operated heatingmandrel. Should, instead of tubes, solid profile have to be extruded,the mandrel (6) is dismantled from the end of the screw and acorrespondingly suited screw discharger is installed. For the extruding,the granular to pulverous plastic-filler mixture is supplied to theinput zone (2) via the supply hopper (12). After supply to the extruder,the material spreads out in the space left by the screw (5) and thegrooved barrel (9) at the beginning of the input zone (2). It is pressedby the rotation of screw (5) into the grooves (14) of the grooved barrel(9) where it is keyed and as a consequence of this process is compressedincreasingly for conveying in the form of a plug in the direction of themouthpiece (10) and accordingly up to the end of the input zone (2). Inparallel with this procedure, the material is adjusted to temperaturessuited to the further processing by the tempering arrangements (8' and8") as already described. The material is immediately forced into theoutput zone (11) and extruded through the mouthpiece (10) under thepressure built up by the screw (5). The material in this zone (11) isadjusted to the desired temperature for the extruding by means of thetempering arrangements (8'" and 8""). This is possible largelyindependently of the temperature of the input zone (2) because, betweenthe last indicated zone and the output zone (11) there exists a thermalbarrier (13). According to a preferred embodiment, when extrudingtubular extrudates the mandrel (6) rotates with the speed of rotation ofthe screw (5). Should the extrudate rotate to an impermissible extent asa result of the friction between mandrel (6) and material connected withthe rotation, the casing inside of the mouthpiece (10) can have, fromthe input side of the material over at least a part of its length,longitudinal grooves (16) extending conically in the extrusion directionwhich are preferably curved in cross section and, have broken edges.Such a constructional form shows the cross section through a tubemouthpiece in FIG. 2. In this Figure, in addition to the temperingarrangement (8"") for the mandrel (6), there are to be seen a mouthpiece holder (18), the tempering arrangement (8'"), an air gap (19) aswell as a sheet metal cladding (20).

                                      TABLE 1                                     __________________________________________________________________________                             EXAMPLE                                                                             EXAMPLE                                                                             EXAMPLE                                                                             EXAMPLE                                                                             EXAMPLE                      PROPERTIES               1     2     3     4     5                            __________________________________________________________________________    Bulk density       (g/cm.sup.3)                                                                        1.98  1.82  1.90  3.53  6.90                         (DIN 51918)                                                                   Specific electrical                                                                       In the pressing                                                                      (Ω · μm)                                                          500   300   90    10     8                           resistance  direction.                                                        (DIN 51911) At right angles                                                                      (Ω · μm)    70                                       to the pressing                                                               direction.                                                        Dynamic e-modulus                                                                         In the pressing                                                                      (kN/mm.sup.2)                                                                       12     9    20    28    7                            (DIN 51915) direction.                                                        Bending resistance                                                                        In the pressing                                                                      (N/mm.sup.2)                                                                        52    40    45    40    31                           (DIN 53455, Prufk.Nr.5)                                                                   direction.                                                        Linear coefficient of                                                                     In the pressing                                                                      (μm/(K · m))                                                            20    17    13    15    35                           expansion (20° C.)                                                                 direction.                                                        (DIN 51902) At right angles                                                                      (μm/(K · m))      48                                       to the pressing                                                               direction.                                                        Thermal conductivity                                                                      In the pressing                                                                      (W/(K · m))                                                                10    30    40    60    60                           (DIN 51908) direction.                                                        Permeability co-efficient                                                                 At right angles                                                                      (cm.sup.2 /s)                                                                         6.10.sup.-6                                                                         3.10.sup.-6                                                                         4.10.sup.-7                                                                         8.10.sup.-5                                                                         6.10.sup.-5                (DIN EN 51935)                                                                            to the pressing                                                               direction.                                                        __________________________________________________________________________     Example 1 = 76.6% by volume Graphite/23.4% by volume PVDF                     Example 2 = 74.4% by volume Graphite/23.7% by volume COCPlastic/1.95% by      volume pressing auxiliary PED                                                 Example 3 = 72% by volume Graphite/28% by volume Novolak                      Example 4 = 78% by volume Titanium/22% by volume Polypropylene                Example 5 = 80% by volume Copper Fibres/20% by volume PVDF               

What is claimed is:
 1. An extruder comprising a product feed device, anouter mouthpiece, and two barrels arranged coaxially between the productfeed device and the outer mouthpiece, the first barrel connected to theproduct feed device and having an inside wall with grooves essentiallyparallel to a longitudinal axis of the first barrel, the second barrelconnected to the outer mouthpiece, a thermal barrier at a transitionfrom the first barrel to the second barrel, a screw arranged in thefirst barrel for conveying material into the second barrel, temperingarrangements for the first barrel, tempering arrangements for the secondbarrel, and measuring and controlling arrangements connected to thetempering arrangements for adjusting the desired operationaltemperatures of the extruder.
 2. An extruder according to claim 1including tempering arrangements for the screw.
 3. An extruder accordingto claim 1 including a mandrel connected to the screw and arranged inthe second barrel.
 4. An extruder according to claim 3 includingtempering arrangements for the mandel.
 5. An extruder according to claim1 wherein the mouthpiece includes a casing with grooves on an insidesurface thereof.
 6. An extruder according to claim 1 including coolingarrangements connected to cool the first barrel in the neighborhood ofthe mouthpiece side end of the first barrel.